A clear picture is imerging. This AM it was pretty warm and the climate control came on right away. Makes me think that the sensor (a) works since there was a change over cold temps and (b) the sensor may be only for the climate control (as suggested by tangofox).

Sounds like only the AC can turn on the aux fan.

When it gets hot, I may try to rig a switch that will allow me to turn on the fan at will.

Thanks for your help.

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1984 300Sd 210k

Former cars:
1984 300D 445k (!!) (Strider) Original (and not rebuilt) engine and transmission. Currently running on V80 ( 80% vegetable oil, 20% petroleum products). Actually not, taking a WVO break.
1993 300d 2.5 275k. Current 120/day commuter
1981 300SD 188k (Hans) Killed by a deer